The present invention relates to controlling a power amplifier by manipulation of the VCC input supply voltage and bias set point, and particularly through manipulation of the VCC input supply voltage and bias set point based on an output power from the power amplifier.
Wireless communication systems enjoy significant popularity, finding widespread use in both developed and developing regions. Indeed, the very popularity of wireless communication systems spurs their development and advancement, driving system designers and service providers to devise ways of supporting more users within a finite radio frequency spectrum. Existing and pending wireless communications standards typically rely on frequency, code, or time-division multiplexing techniques that allow multiple users of mobile terminals (such as cellular phones) to share the same frequencies within a given service area. Commonly, such access schemes benefit from each mobile terminal controlling its transmitted signal power to help minimize its interference with other active devices in a given wireless service area.
This power control approach presents mobile terminal designers with significant challenges. For example, power control techniques typically require transmit signal amplifier circuits that provide a range of transmit signal gain. This allows the mobile terminal to transmit with a desired signal power based on adjusting the gain of one or more such transmit signal amplifier circuits. For example, as the mobile terminal moves closer to a supporting base station, the wireless communications systems may instruct the mobile terminal, via control signaling, to reduce its transmit power. Essentially, in such wireless communications systems, active mobile terminals are controlled such that they transmit with the minimum necessary signal power at all times.
During this power control activity, the power amplifier may operate at less than full output power to provide the desired continuous transmit signal gain. Unfortunately, when operating at less than full output power, many power amplifiers are not efficient and power is wasted. Because mobile terminals are typically battery-operated, power consumption is of great concern for these devices. Any technique that could extend battery life to provide longer talk time is to be appreciated.
In the past, Doherty amplifiers, load switches and segmented output stages have been used to address efficiency concerns. To date, only the Doherty configuration has provided automatic efficiency compensation as the power is backed off. The other approaches require the intervention of an external controller. These approaches leave something to be desired in terms of simplicity, cost, and results.
The present invention takes a signal proportional to the RF output power of a power amplifier and controls a DC-DC converter that supplies DC power to a power amplifier, thereby increasing the efficiency of the power amplifier. Specifically, a signal proportional to the output of the power amplifier is used to control the DC-DC converter, thereby controlling the DC power supplied to the power amplifier. A second signal proportional to the output of the power amplifier may control a bias circuit, thereby changing the bias point of the power amplifier.
In a first embodiment, the signal proportional to the output of the power amplifier is created by rectifying a sample of the output signal from the power amplifier. In a second embodiment, the signal proportional to the output of the power amplifier is created by using a power sensed output and a power sensed reference output available on some power amplifier circuits.
The signal proportional to the output of the power amplifier may be used not only to control the DC-DC converter, but also may control a bias control circuit associated with the power amplifier. In one embodiment, a control processing circuit makes the bias control signal a function of the control signal for the DC-DC converter, and the two control signals cooperate to change the bias provided to the power amplifier concurrently with the power control signal to control the power amplifier in a coordinated fashion to increase efficiency.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.